1. Field of the Disclosure
The present disclosure relates to an array substrate for a liquid crystal display device, and more particularly, to an array substrate for an in-plane switching mode liquid crystal display device where two-dimensional brightness and three-dimensional brightness are improved and a three-dimensional image display device including the array substrate.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device uses an optical anisotropy and polarization properties of liquid crystal molecules to produce an image. Due to the optical anisotropy of the liquid crystal molecules, refraction of light incident onto the liquid crystal molecules depends upon an alignment direction of the liquid crystal molecules. The liquid crystal molecules have long thin shapes that can be aligned along specific directions. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field. Accordingly, the alignment of the liquid crystal molecules changes in accordance with a direction of the applied electric field and the light is refracted along the alignment direction of the liquid crystal molecules due to the optical anisotropy, thereby images displayed.
Among various types of LCD devices, an active matrix type liquid crystal display (AM-LCD) device has been the subject of recent research due to its high resolution and superior quality for displaying moving images.
The LCD device includes a color filter substrate having a common electrode, an array substrate having a pixel electrode, and a liquid crystal layer interposed between the color filter substrate and the array substrate. In the LCD device, the liquid crystal layer is driven by a vertical electric field between the pixel electrode and the common electrode. Although the LCD device provides a superior transmittance and a high aperture ratio, the LCD device has a narrow viewing angle because it is driven by the vertical electric field. Accordingly, various other types of LCD devices having wide viewing angles, such as in-plane switching (IPS) mode LCD device, have been developed.
FIG. 1 is a cross-sectional view of an IPS mode LCD device according to the related art.
In FIG. 1, an upper substrate 9 and a lower substrate 10 face and are spaced apart from each other. A liquid crystal layer 11 is interposed between the upper and the lower substrates 9 and 10. The upper substrate 9 and the lower substrate 10 may be referred to as a color filter substrate and an array substrate, respectively. A common electrode 17 and a pixel electrode 30 are formed on the lower substrate 10. The liquid crystal layer 11 is driven by a horizontal electric field “L” between the common electrode 17 and the pixel electrode 30.
FIGS. 2A and 2B are cross-sectional views showing ON and OFF states, respectively, of an IPS mode LCD device according to the related art.
In FIG. 2A, voltages are applied to a pixel electrode 30 and a common electrode 17 to generate an electric field “L” having horizontal and vertical components. First liquid crystal molecules 11a of the liquid crystal layer 11 over the pixel electrode 30 and the common electrode 17 are not re-aligned by the vertical component of electric field “L,” and a phase transition of the liquid crystal layer 11 does not occur. Second liquid crystal molecules 11b of the liquid crystal layer 11 between the pixel electrode 30 and the common electrode 17 are re-aligned by the horizontal component of electric field “L,” and a phase transition of the liquid crystal layer 11 occurs. Because the liquid crystal molecules are re-aligned by the horizontal component of the electric field “L,” the IPS mode LCD device has a wide viewing angle. For example, users can see images having a viewing angle of about 80° to about 85° along top, bottom, right and left directions with respect to a normal direction of the IPS mode LCD device.
In FIG. 2B, an electric field having a horizontal component is not generated when voltages are not applied to the IPS mode LCD device. Thus, first and second liquid crystal molecules 11a and 11b are not re-aligned, and a phase transition of the liquid crystal layer 11 does not occur.
FIG. 3 is a plan view showing an array substrate for an IPS mode LCD device according to the related art.
In FIG. 3, a plurality of gate lines 43, a plurality of common lines 47, and a plurality of data lines 60 are formed over a substrate 40. The plurality of gate lines 43 are parallel to the plurality of common lines 47 and cross the plurality of data lines 60 to define a plurality of pixel regions P. A thin film transistor (TFT) Tr is a switching element connected to the gate line 43 and the data line 60 and is formed in each pixel region P. The TFT Tr includes a gate electrode 45, a gate insulating layer (not shown), a semiconductor layer (not shown), a source electrode 53 and a drain electrode 55. The gate electrode 45 is a portion of the gate line 43 and the source electrode 53 is connected to the data line 60.
A passivation layer (not shown) is formed on the TFT Tr. In addition, a plurality of pixel electrodes 70a and 70b and a plurality of common electrodes 49a and 49b are formed on the passivation layer in the pixel region P. The plurality of pixel electrodes 70a and 70b are connected to the drain electrode 55 through a drain contact hole 67 in the passivation layer, and the plurality of common electrodes 49a and 49b are connected to the common line 47. The plurality of pixel electrodes 70a and 70b are parallel to and alternately disposed with the plurality of common electrodes 49a and 49b. 
The pixel region P of the substrate 40 has a mono-domain structure where liquid crystal molecules in the pixel region P are aligned along one direction. As a result, a color shift phenomenon such that an undesired color image is displayed occurs along top, bottom, right and left directions with respect to a normal direction of the IPS mode LCD device. For example, a yellowish image may be displayed when the IPS mode LCD device is viewed along a top-left direction (10 o'clock), and a bluish image may be displayed when the IPS mode LCD device is viewed along top-right direction (2 o'clock). Accordingly, a display quality of the IPS mode LCD device is deteriorated.
For the purpose of improving the above disadvantages, an IPS mode LCD device of a two-domain structure has been developed where a plurality of pixel electrodes and a plurality of common electrodes have a bent part at a center portion of a pixel region.
FIG. 4 is a plan view showing an array substrate for an IPS mode LCD device having a two-domain structure according to the related art.
In FIG. 4, a plurality of gate lines 103, a plurality of common lines 109 and a plurality of data lines 115 are formed over a substrate 101. The plurality of gate lines 103 are parallel to the plurality of common lines 109 and cross the plurality of data lines 115 to define a plurality of pixel regions P. A thin film transistor (TFT) Tr is a switching element connected to the gate line 103 and the data line 115 and is formed in each pixel region P.
A plurality of pixel electrodes 170 and a plurality of common electrodes 173 are formed in the pixel region P. The plurality of pixel electrodes 170 are connected to the TFT Tr, and the plurality of common electrodes 173 are connected to the common line 109. The plurality of pixel electrodes 170 are parallel to and alternately disposed with the plurality of common electrodes 173.
Each of the plurality of pixel electrodes 170 and the plurality of common electrodes 173 has a bent part at a center portion of the pixel region P so that the IPS mode LCD device can have a two-domain structure where liquid crystal molecules in an upper half of the pixel region P are aligned along a first direction and liquid crystal molecules in a lower half of the pixel region P are aligned along a second direction different from the first direction. In the IPS mode LCD device having a two-domain structure, a color shift phenomenon along top-left, top-right, bottom-left and bottom-right directions is prevented by compensation of the two domains.
Recently, a switchable display device where a two-dimensional image and a three-dimensional image are selectively displayed has been suggested. In addition, a switchable display device using an IPS mode LCD device as a display panel has been researched. However, when the IPS mode LCD device according to the related art is applied to the switchable display device, a display quality such as brightness of a two-dimensional image and a three dimensional image is deteriorated.
The switchable display device may include a display panel and a retarder delaying a phase of light for displaying a three-dimensional image. A right-eye image and a left-eye image are alternately displayed in the display panel and the retarder is spaced apart from the display panel by a gap distance. While a width of a pixel region of the display panel for the two-dimensional image is determined regardless of the gap distance, a width of a pixel region of the display panel for the three-dimensional image is determined based on the gap distance. Accordingly, a width of the pixel region and a width of a border region between the pixel regions for the two-dimensional image are different from a width of the pixel region and a width of a border region between the pixel regions for the three-dimensional image. For example, a width of the border region between the pixel regions for the three-dimensional image may be greater than a width of the border region between the pixel regions for the two-dimensional image.
As a result, when the pixel region and the border region of the display panel are designed for the three-dimensional image, the width of the border region excessively increases for the two-dimensional image and brightness for the two-dimensional image decreases.